It's worth the considerable trek to the southern part of the city to tour around the campus of UNAM, the National Autonomous University of Mexico, to see its iconic mid-20th-century buildings.
American writer Selden Rodman, touring Mexico in the 1950s, wrote that the UNAM library "is one of the dozen most exciting buildings in the world... [n]ot merely because it was the first to be surfaced entirely with mosaics, but because the mosaics form a stunning geometry of color in the sunlight- even from miles away." More than half a century later, the mosaic-stippled building, made by Mexican artist Juan O'Gorman, continues to impress.
It's not the only structure on campus worth visiting, however. Neighboring buildings and structures are equally compelling, including the Olympic Stadium on the campus, which features a mural by Diego Rivera.
University City, as the campus is called, was inscribed by UNESCO onto the World Heritage Site list in 2007.

If you fall in love with Mexico City (and I'm warning you, it's hard not to) and you want to stick around for some long-term language learning, there are several schools where you can enroll in either a certificate or degree-granting program.
One of the most obvious choices is UNAM, Mexico's most prestigious university and one of the most esteemed institutions of higher learning in Latin America. The university offers dozens of degree programs at the bachelors, masters, and doctoral levels.
If you're interested in a shorter-term commitment, consider one of the certificate or degree programs offered by Casa Lamm (primarily literature and arts-focused) or Le Cordon Bleu's Mexico school, which offers certificates in Mexican cooking, pastry-making, and wine, as well as a masters-level program in hospitality and service.